HPPM stripes (polypropylene) were utilized in concrete as a crack-resistant improvement material. The HPPM is constructed of plastic polypropylene fibers, according to the producers. It also has a high level of chemical stability and strength. By volume, fiber content ranged from 0.5 % to 2.5 %. HPPM were chopped into little pieces of one centimeter in length and one centimeter in width. The physical parameters of the single-use HPPM are listed in Table 4.
Table 4
Physical properties of healthy personal protective materials (HPPM) Shabrian et al., 2021.
Physical properties
|
SHM
|
Standard
|
Specific gravity
|
0.91
|
ASTM D792-20 (2020)
|
Melting point (Co)
|
160
|
ASTM D7138-16 (2016)
|
Water absorption 24 h (%)
|
8.8
|
ASTM D570-98 (2018)
|
Tensile strength (MPa)
|
3.65
|
ASTM D638-14 (2014)
|
Tensile strength at break (MPa)
|
3.97
|
ASTM D638-14 (2014)
|
Elongation at break (%)
|
118.9
|
ASTM D638-14 (2014)
|
Rupture force (N)
|
19.46
|
ASTM D638-14 (2014)
|
Aspect ratio
|
24
|
---
|
4.1.xrd And Sem Of Hppm Stripes
Figure 2a, b shows the face mask and HPPM fibers' integrated X-ray diffraction patterns. The diffraction peaks of all fibers were obtained between 10 and 30 degrees, as shown in the Fig. 2b. The peaks obtained at approximately 14 o, 17o, 18.6o, 21–22 o, and 28 o are similar to the peaks generated by -polypropylene (JCPDS 00-050-2397- 1970). Any micro structural changes in HPPM were observed using SEM. The HPPM layer (polypropylene) was sliced into a 10 mm x 10 mm size and examined using a SEM (Hitachi, TM3000) at 1000 magnification. Figure 2c shows structural changes in polypropylene fibers such as melting, distortion, tangling, and cracking.
4.2.XRD results of concrete containing the HPPM fibers.
Specimens were studied using XRD to show the influence of adding HPPM Fibers to concrete mixtures on phase changes. Figure 3 shows the results of a 2 % HPPM test at the age of 28 days. The crystalline phase, i.e. portlandite Ca(OH)2, calcite Ca(CO)3, and silicon dioxide SiO2, are the primary peaks. Ca(CO)3 and Ca(OH)2 levels did not change appreciably when HPPM fibers were added. Similarly, when fibers are added, it is represented at 650. This phenomenon demonstrates that fibers are incapable of participating in chemical processes. Furthermore, the presence of amorphous materials may be indicated by the convex form between 2theta = 16° and 36°.
4.3. Slump
Figure 4 depicts the slump values for concrete mixtures including various amounts of HPPM as an addition. Slump values are anticipated to decrease linearly as the percentage of HPPM added to concrete increases. In comparison to the reference slump of the reference sample, the slump has decreased by approximately 5%, 13%, 20%, 30%, and 43%, respectively. The decreased slump could be attributed to the HPPM particles' heterogeneity and roughness, which could diminish the fluidity of the mixtures as well as HPPM's high absorption (8.8%) Fig. 4. Because of HPPM's high porosity (avg. 8.8%) and high cohesiveness between HPPM and concrete matrix (Das CS, et al. 2018), increasing the amount of HPPM resulted in lower slump values. The volume, form, and slenderness of the fibers, as well as the mix composition, influence the workability of concrete (Markovic, 2006, Karahan and Atiş, 2011 Zych and Krasodomski 2016, Wan Ibrahim 2017, Blazy and Blazy 2012). When the fiber dose exceeds this crucial amount, the likelihood of fiber clamping or balling increases, resulting in uneven fiber distribution and a greater reduction in flowability (Ranjbar and Zhang, 2020).
4.4.compressive Strength (Ucs)
The UCS of the samples is shown in Fig. 5. The control mix in the experiment had a 28-day UCS of 448Kg/Cm2, but a 2% addition of shredded HPPM by volume produced the best results. In UCS to the control mix study, UCS increased steadily between 1% and 1.5 % before falling marginally at 2.5 %. In comparison to the control sample, volume increments of 0.5 %, 1%, 1.5 %, and 2% resulted in sample increases of 8.82, 11.05, 13.68, and 9.40 %, respectively (Fig. 5). As a result, the findings show that incorporating HPPM into concrete had a significant impact on the UCS of the mixture. Xu et al., 2020, reported similar results in UCS, where the addition of different plastic fibers boosted UCS to the point where it began to fall. The improvement in UCS with the additional content of polypropylene fibres may be related to the fiber's crack restriction effect, as demonstrated in earlier investigations (Nili and Afroughsabet, 2010). According to the study by Mohammadhosseini et al., the declining trend at 2.5 % could be owing to the presence of voids at 2.5 % and the existence of weakening interfacial connections between the cut-up HPPM and the cement (2017).
When the fiber dosage was raised from 0 % to 3 %, the UCS increased by 6% (Ravinder et al 2019). In other circumstances, such as (Ahmed et al 2020), fc rose until a specified fiber content value was reached and subsequently reduced. This could be due to poor workability induced by too many fibers and an increase in air content (Gencel et al 3011) and porosity (El-Newihy et al 2018).
The addition of HPPM to the mixtures, on the other hand, considerably modified the concrete's failure mode from brittle to ductile, as seen in Fig. 6. The specimens did not crush because of the bridging effect of the HPPM fibers, and they maintained their integrity until the completion of the test. It was discovered that mixtures containing HPPM had lower compressive strength at an early age, but that after a longer period of curing, they had a higher compressive strength. This suggests that the bridging imacte of fiber can improve UCS of the concrete over time.
4.5. Nondestructive Wave Velocity (Pv)
At the age of 28 days, an ultrasonic test was performed on water saturated cubic concrete specimens of 150 mm to assess the number of internal pores in the specimens. This non-destructive test uses reflected waves that have radiated between probes to assess the permeability of a specimen, according to ASTM C597. The test was performed by crossing the two faces of the specimen with the instrument's two probes. The PV test is a nondestructive method for determining concrete's consistency and efficiency. Concrete cracks and pores are also referred to as PV (Ahmmad, et al., 2016). Non-destructive testing is a good way to assess the quality of concrete. The PV test's effects are depicted in Fig. 7a. PV grew consistently as HPPM content by volume climbed until the volume crossed 2.0 %, after which it declined marginally to 2.5 %, as seen in the data. Similarly, to UCS, the HPPM material with a volume of 2.0 % produces the best results. According to Sims et al., (2019) and Khatib et al., (2019), concrete with a PV result more than 4500 m/s is considered very good to outstanding concrete with a high-quality rating. The quality of the concrete fell once more at the 2.5 % volume mark when compared to the control specimen for the experiment; nonetheless, it should be noted that the quality of the concrete improved in all mix designs, signifying beneficial features. According to Yap et al., (2013), good quality concrete has no substantial voids or cracks in the ranges mentioned; consequently, as proven in research by Shen et al., (2020), the usage of shredded face masks reduced the amount of microcracks in the concrete, thereby enhancing the overall quality of the concrete. No voids or cracks can jeopardize the structural integrity of the concrete within the above-mentioned limit. Due to an increase in void content and hence porosity with increased fiber, PV values tend to drop beyond a fibere composition of 2.5%. According to BIS, the UPV measurements range between 3.8 and 4.04 Km/sec, indicating that the concrete quality is good (IS 13311-1) (1992). HPPM was added to the equation, which increased the UPV values up to a particular volume fraction. However, as expected, increased HPPM stripes content resulted in lower UPV values. This decrease in change of velocity is thought to be owing to the existence of voids and microcracks in the concrete specimens, which reduced homogeneity at higher fiber volume fractions. For specimens containing HPPM at any %, UPV values ranging from 4200 to 4600 m/s were discovered, and it was regarded as good quality concrete.
The values of ultrasonic pulse velocity have been shown to be connected to their matching cube compressive strength. The relationship between UCS and UPV values of concrete mixtures including HPPM fiber have a strong relationship, as seen in Fig. 7b. A power regression method was used to correlate the experimental results, with an R2 of 0.872 for all samples, indicating a high level of confidence in the association.
4.6. Sorptivity
The findings of the (S) are shown in Fig. 8. When fiber concretes are compared to ordinary concrete, the (S), which is a measure of concrete durability, is lower. It's possible that the loss of connection in the pore space is caused by HPPM fibers filling porosity (Ramezanianpour et al 2013). The minimum (S) for 2 % HPPM is 2.55(106) (m/s), whereas the maximum value for 2.5 % HPPM is 3.46 (m/s). Furthermore, every HPPM concrete has a lower (S) than the control mix, despite the fact that the high value for 2.5 % HPPM is similar to a mix with a lot of porosity. This result demonstrates a considerable reduction in capillary (n) and inner conductivity of pores when HPPM fibers are used, and it confirms all of the other durability findings in this study.
4.7. The Flexural Strength
The FS of UCS and PV follows the similar pattern, with a rise up to 2 % HPPM fibre content and then a reduction as the number of fibres increases. The results shown in this graph show that, similar to tensile strength, concrete flexure strength increased as the HPPM concentration increased. In comparison to the control mix, specimens with HPPM of 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 % had FS of 17.8 %, 24 %, 27.5 %, 33.4 %, and 1.6 %, respectively. Furthermore, HPPM played a vital role in the development of FS, particularly after a longer duration of water curing. The overall effect of HPPM appears to be geared toward increasing FS, as evidenced by a 33.4 % increase in flexural strength in concrete with 2.0 % of HPPM. The drop in FS values as fiber content increases can be due to the fact that voids in the matrix grow as 2.5 % HPPM fibres are added to the matrix. As a result of applying HPPM to sustainable concrete, the sample's FS was considerably boosted. As a result, further FS enhancements may be accomplished by introducing HPPM with an optimized geometric shape to create better concrete FS. The adoption of mechanically enhanced fibers with increased bond strength should result in more resilient structural concrete capable of producing bigger residual capacities as a result of developments in recycled HPPM processing.
The fibers intersecting the cracks in the tension zone of the specimens caused the rise in FS. HPPM fibers flex to hold the crack face separation, offering a larger energy absorption capacity and stress relaxing the micro-cracked area adjacent to the crack tip (Fig. 9a, b). Increased fiber content, on the other hand, resulted in reduced FS. This issue could be caused by the concrete's decreased workability at larger volume fractions in the combinations. The recorded FS of prismatic beams are shown in Fig. 9c.
4.8. Impact Strength
In terms of the number of blows required to cause the concrete specimen to collapse, the IMs of concrete was investigated for different volume fractions of HPPM fiber. PPF improves the impact resistance of concrete (Feng et al 2018). The addition of just 1% micro PPF increased the number of blows till failure by nearly thrice (Widodo 2012). The number of blows at first crack was assessed to be 76, 35, 546, 654, 987, and 698 percent for 0 percent, 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 % of HPPM, respectively, when HPPM was added to concrete mixtures. Furthermore, with 0 %, 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 % of HPPM, the number of strikes required to destroy the sample increased 3.0, 3.3, and 4.8 times, respectively (Fig. 10). These findings are consistent with (Jain et al 2011), which found that the number of blows for failure increased from 76 (100%) for ordinary concrete to 355 (367.105%), 546 (618.421%), 654 (760.526%) 987(1198.68%), and 689 (818.421%) for concrete with HPPM fibers equal to 0 %, 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 %, respectively, for concrete with HPPM fibers equal to mix control (Fig. 10).
4.9. Spalling resistance
Furthermore, when compared to concrete without fibers, the proportion of spalling for PPFRC is lower (Broda 2016). It is the outcome of the advancement of fire protection. HPPM melts at 160 degrees Celsius, while spalling occurs at 190 degrees Celsius (Olgun, M., 2013). As a result, as the fibers melt, empty channels emerge and a new pathway for gas to escape is generated. At the same time, it lowers the internal pore pressure. These findings have also been confirmed in publications by Kalifa et al. (2020), Algourdin et al. (2020), and others (2020). Finally, HPPM considerably improves the fire resistance of concrete.
4.10. Abrasion Resistance
It's worth noting that using HPPM fibers improves concrete's abrasion resistance. Horszczaruk (2012) demonstrated that after including 0.9 kg/m3 of fibers, the mean depth of wear for HPPM fell from 29 to 42 % as compared to plain concrete. The increase in abrasion resistance for concretes containing fibrillated 0 %, 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 %HPPM varied from 6.4 %, 5.7 %, 4.9 %, 3.7 %, and 4.6 %, depending on the water to cement ratio (Grdic et al 2012).
This phenomenon can be explained by the fact that incorporating HPPM fibers into concrete inhibits the creation of cracks and effectively diminishes the concrete's intrinsic cracking tendency. Furthermore, the pore blocking effect of HPPM fibers causes the pore structures in hardened concrete to become more detached, resulting in less capillary porosity and lower water penetration of the concrete. In addition, HPPM's abrasion resistant strength is improved. On the resistance to abrasion damage, HPPM fibers outperform control concrete (Fig.11).
4.11. Water absorption and porosity
The resistance of concrete to the intrusion of hostile ions is another important aspect that influences its durability. The porosity of concrete is indirectly represented by its absorption characteristics, which also provide useful information regarding the permeable pore volume within the concrete and the connectivity between these pores. Ozbakkaloglu and Afroughsabet (2015). The percentage of Sw is a measure of pore volume or (n) of concrete after hardening, and it is one of the fundamental factors of concrete durability.
When it comes to water absorption, many studies show that HPPM absorbs less water than plain concrete (Li and Liu 2020). According to Afroughsabet and Ozbakkaloglu (2015), regular concrete absorbs 1.52 % of water, but concretes containing 1.5, 3.0, and 4.5 % PPF absorb 39, 46, and 49 %of water, respectively. Similarly, in (Behfarnia, Behravan 2014), the water absorption was reduced by roughly 45 %, from 2.481 %to 1.366 %. PPFRC absorbed 24.7 %less water than concrete without fibers in tests (Bolat et al 2014). This could be due to the fibers' action limiting the number of cracks to a minimum. Fibers, on the other hand, have been shown in some tests to have a negative impact on absorbability.
The findings show that injecting HPPM into concrete reduced concrete's Sw significantly. When compared to the respective values obtained from control concrete mixes, water absorptions of concrete mixes with 0 % 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 % HPPM decreased by 25% and 36%, respectively. The results of polypropylene HPPM fiber-reinforced concretes show that HPPM fibers have a favorable effect on reducing concrete water absorption. As shown in Fig.12 a, increased fiber content resulted in a greater reduction in water absorption. As a result, among all HPPM fiber-reinforced concretes evaluated in this study, the combination containing 2% HPPM fiber had the lowest water absorption. Adding fibers to concrete provides a variety of advantages, but it also causes the thickness of the transition zone to rise in hybrid fiber-reinforced concretes.
The influence of HPPM on porosity cannot be clearly measured, as seen in Fig.12 b. Workability is influenced by a number of factors, one of which being the distribution of fibers within the mixture and the level of porosity. There have been studies that show that when the fiber dosage increases, the porosity increases (Fallah and Nematzadeh 2016). Porosity can decrease with the addition of fibers confined to a lower amount, then increase again with bigger fiber additions, as shown in (Ismail, M. Ramli 2016). The porosity of concrete with 0 %, 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 %HPPM varied between 4.9 %, 4.3 %, 5.2 %, 3.6 %, 4.3 %, and 5.5 %in the current study. A summary of how HPPM fiber incorporation affects concrete porosity (Fig.12 b). The findings of this study show that adding more than 2.5 % of the HPPM fibers to concrete results in increased transition zone thickness and (n), and hence higher Sw. The increased porosity could be due to poor compaction, which could lead to more micro-cracks, unrestrained fibers, and cracks, as well as poor fiber-matrix bonding (Mohammadhosseini, and Yatim 2017).
4.12. Water penetration and permeability
Because of the pore blocking action of HPPM fibers, all water penetration depths for HPPM are lower than for control mix. The findings support the accuracy of HPPM readings.
The specimen with 2% HPPM fiber content has a minimum depth of penetration of 7.4 mm, which is 38.33 %less than the control mix. The drop in HPPM depth of water penetration and then increase (11.6 at 2.5 %) could be attributable to an increase in “n” as the HPPM fiber content increases. In fact, the 2% decrease in water depth is most likely attributable to pore blockage and decreased capillary porosity. This result backs up the results of the other durability tests presented in this article. Figure 13 shows the findings depth of water penetration at the age of 28 days.
In addition, the impact of HPPM fibers on permeability is not well understood. In their study, Islam and Gupta (2016) found that adding PPF to concrete increases both water and gas permeability. Hager et al. reported a similar finding in their paper (2019). Many researches, on the other hand, discovered that fibers have a favorable effect on permeability. According to Zhang and Li (2013), adding PPF to concrete reduced the duration of water permeability. Similarly, samples with fibers demonstrated poorer permeability than samples without them in (Kakooei et al 2012). There have also been studies that show that permeability declines as the volume of fibers grows up to a certain point, then increases and sometimes exceeds that of plain concrete (Flores Medina et al 2015). This is usually due to a lack of workability and an excessive amount of fibers in the mixture.
The presence of HPPM fibers in the concrete reduces the likelihood of the concrete to break by limiting the formation of cracks. Fibers also cause the pore structures in hardened concrete to become more separated, resulting in lower capillary porosity and concrete water penetration.